An NFC (Near Field Communication) enabled device is an example of a communications device that communicates via inductive coupling. NFC is a short-range wireless technology that allows communication between NFC enabled objects over a distance of less than 10 cm. NFC is based on Radio Frequency Identification (RFID) standards. It is a technology that is designed to make an easier and more convenient world for us, enhancing the way we make transactions, exchange content and connect devices. The NFC tags one might see or create include contacts, URLs, map locations, text and much more.
An NFC-enabled device can operate in various operating modes, such as reader/writer mode, card emulation mode, and peer-to-peer mode. For example, an NFC-enabled device in reader/writer mode can behave like a simple contactless card reader. It initiates communication by generating a magnetic field and then sending a command to the target. The target responds to the interrogator by retro-reflecting the incident wave. The specificity of NFC operating modes is that the target can be not only a tag or a contactless card, but also an NFC-enabled device that behaves like a contactless card (in card emulation mode). Usages of reader mode, for example, include information reading, when an NFC-enabled device is used to read data by waving it in front of electronic labels available on streets, bus stops, sightseeing monuments, ad banners, parcels, products or on business cards (vCard). But there are many other possible use cases.
As another example, an NFC-enabled device in card emulation mode can allow the NFC-enabled device to act like smart cards, allowing users to perform transactions such as purchases, ticketing, and transit access control with just a touch. An NFC-enabled device in card emulation mode can be configured for either passive load modulation (PLM) or active load modulation (ALM). While, ALM is typically more complex than PLM, components for implementing ALM in a card-mode device (e.g., a mobile device) can be more compact and, because the card-mode device utilizes a power source to generate a magnetic field rather than just modulate a magnetic field created by a reader, an ALM card-mode device can have greater communications range than a PLM card-mode device.
As a further example, peer-to-peer mode enables two NFC-enabled devices to communicate with each other to exchange information and share files, so that users of NFC-enabled devices can quickly share contact information and other files with a touch.
In all these modes and other possible applications, where an NFC-enabled device is transmitting signal, it can be important to have an accurate transmitter output. As such, there are strong motivations to control the transmitter output with enhanced accuracy.